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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 20 June 2010 by John Cook

Yesterday, we looked at Jo Nova's #1 "killer blow" in her Skeptics Handbook: the tropospheric hot spot. Today, we move onto the Handbook's #2 point: the CO2 lag. When we look through the ice core record, we see that in the past, CO2 levels change after temperature change. From this, Jo Nova argues that CO2 warming is a minor force. But this doesn't give you the full picture. A number of measurements find extra CO2 is trapping heat. So the full body of evidence gives us two facts: warming causes more CO2 and more CO2 causes warming. Put these two together and you get positive feedback.

How does this work? When the Earth comes out of an ice age, the warming is initiated by changes in the Earth's orbit. As the ocean warms, the solubility of CO2 in water falls. This causes the oceans to give up more CO2 into the air. This has several effects. Firstly, the relatively weak warming from orbital changes isn't enough to take our climate out of an ice age. The extra CO2 in the atmosphere amplifies the original warming. That's the positive feedback.

Secondly, CO2 from the ocean mixes through the atmosphere, spreading the warming across the globe. Ice cores and marine sediments find that initial warming begins in Antarctica. Around 800 years later, CO2 rises and at the same time, warming spreads to the tropics and northern hemisphere (Cuffey 2001, Caillon 2003, Stott 2007).

This amplification and spreading of the warming also works in reverse when the planet enters into an ice age. A new paper published over the last week uses ocean sediments to construct a temperature record over the past 2.7 million years (Herbert et al 2010). They find that when ice sheets spread in the Northern Hemisphere, this cools the northern oceans. The result is the oceans absorb more CO2, leading to a dramatic drop in atmospheric CO2. This amplifies the cooling and spreads it across the globe.

A common misconception is that positive feedback always means runaway warming. This isn't necessarily the case. If the feedback is not too great, what happens is an amplification of initial warming with the temperatures eventually stabilising at a higher level. Think a bank account with compound interest - no bank will offer so much interest that you experience runaway interest income. Past history indicates this is the case with our climate - net positive feedback amplifies initial warming but climate settles at a higher temperature. There's a good demonstration of how this works in a past comment by Ned Flounders.

So the CO2 record is entirely consistent with the warming effect of CO2. In fact, CO2 warming explains both the dramatic changes in temperature in the Earth's past and how temperature change is able to spread from the poles to the rest of the globe. Studies comparing past co2 to temperature find a positive feedback relationship (Scheffer 2006). The CO2 lag doesn't disprove the warming effect of CO2. On the contrary, it provides evidence of a climate positive feedback.

Comments

Note that to get the magnitude of the glacial-interglacial CO2 feedback, you need other feedback processes such as wind-driven mining of CO2 out of the deep ocean. The solubility feedback itself is relatively weak and somewhat offset by the salinity-gas feedback. See this post and the Sigman/Boyle and Anderson et al. pieces linked inside.

I think there is a general failure on Science's part to provide a clear explanation, to wit, We know: CO2 causes warming; CO2 is really high; and Warming isn't that bad. Therefore science is wrong about something.

It's the lag of warming behind CO2 that isn't clear, and that creates misunderstanding and doubt in the larger message. An analogy might be helpful, but find one message and repeat it often and succinctly.

A supertanker analogy might make it easier to visualize, and this is not a good one, but I hope a clear explanation could be crafted--

Earth's climate is slow to change, because it is massive, and many inputs drive changes. CO2 is one driver, and a very powerful one. Imagine the climate to be a huge supertanker. CO2 is pushing the engines faster and faster toward a hotter climate. Today, the climate is already measurably more extreme. Science is warning us to pull back the throttles before the ship runs aground. Even if we cut the throttles to zero today, it will take time for the ship to slow, and the longer we wait, the faster the tanker will be going.

I was with you guys in doubting Hocker's assertion that temperature is driving CO2 concentration in the atmosphere over the short term.

Now you are asserting that over the medium term (700,000 years) that CO2 is somehow a significant factor in the Ice Age cycle even though it lags temperature by ~900 years. Give it up, your convoluted arguments don't make sense.

Science is never settled; but once in awhile an event occurs which gives us the opportunity to test some of our hypotheses.

The Gulf of Mexico disaster is releasing ~2 to ~3 million gallons of oil every 24 hours depending upon who does the estimate. John Kessler at A&M estimates that 40% of the leak is Methane. I think one needs to add 40% to account for the methane; in either case, I believe enough Methane has leaked into the atmosphere in a short enough period of time to generate a blip at best which will be difficult to explain away as non-Anthropogenic.

GC, it's a rare and wonderful thing to see a premise so obviously wrong that we can all agree. This one's a bit more complicated but you're smart enough to tell us, what's your specific objection? Further reading here where John covered the lag before, also it's covered here at Real Climate as well as here at New Scientist.

Same misunderstanding patiently explained by a bevy of authors. It's been in circulation for at least 5 years now, time to let it die peacefully.

DrTom #4, Are you referring to last weeks news that perhaps for every barrel of oil 2900 cubic feet of natural gas is escaping from the well?

Given the depth of the wellhead, most methane should dissolve before reaching the surface as described in a previous post about methane venting from the East Siberian Arctic Shelf.

If the estimates are correct then the amount of methane gas released is staggering. Will this gas ultimately be deposited as clathrate on the bottom of the GOM or will it slowly outgass to the atmosphere?

5) More warming leads to more CO2 being released from the oceans. We've got positive feedbacks now. Go to #3.

6) Eventually a new climate equilibrium is reached.

In short, Milankovitch cycles start the warming, which eventually releases CO2 from the oceans (the 800 year lag), which leads to more warming, which in turn releases more CO2. The whole process takes thousands of years.

The comment in the article, "A common misconception is that positive feedback always means runaway warming. This isn't necessarily the case. If the feedback is not too great, what happens is an amplification of initial warming with the temperatures eventually stabilising at a higher level." sounds misleading at best.

Now I have to admit that my own memories of positive feedback in electronics circuits is somewhat vague, but what I recall is: in-phase positive feedback DOES cause unlimited growth, which is exactly why the circuit designer tunes the feedback loop to limit the gain/oscillation to a useful value. This is done in one of two ways 1) adjust the phase of the feedback or 2) decrease the gain of the positive feedback as the circuit output approaches the desired value.

Which one of these is the best analogue for what happens with positive feedback in climate?

In particular, I wonder in the citation above: once it "stabilizes at a higher level" is the feedback even still positive? Isn't it changing throughout that time, stabilizing only when the feedback drops, so that it is no longer 'positive'?

As usual you have left out the detail to create an inconsistent argument.

AGW proponents claim that current warming will/is releasing methane from arctic areas to warm the Earth. If so, this must also occur at the end of Ice Ages, but it is never mentioned, so as not to get in the way of the 'c02 explanation' for the end of Ice Ages.

Methane release must occur as the sun has warmed the earth since 1750-1950+, which is also conveniently not mentioned, so as to not get in the way of the c02 warming effect of the late 20th century.

Also, the warmign oceans at the end of ice ages must store all that 'missing ocean heat', which is then slowly released, as AGW proponents claim it will do over the coming century.

You also have ice albedo changes as Ice ages end, vegetation changes, and ocean current changes. All of these are not mentioned in the above article, so as to bolster the effects of C02, but they are usually mentioned whenever AGW proponents want to enhance projected T effects over the next century.

Cynicus, #6. Aloha. Yes, I will take those numbers for the sale of argument. Hot Methane escaping under pressure won't form clathrate unless it is contained at depth. Some will certainly dissolve to form anoxic zones but most will bubble up and enter the atmosphere.

Methane is considered ~25 times stronger than CO2 as a greenhouse gas over a 100 year time frame; but over 20 years it's GWP is 72 and over 8 years a large release should have a noticeable effect, possibly in the form of a rapid-onset extinction event.

Given the short-term 72-to-1 greenhouse potential of CH4 to CO2, we can guesstimate that within a short period of time we will have tossed the equivalent of an extra year of CO2 into the atmosphere from the Gulf and it will persist for 8 years. If it raises the average global temperature by just ONE degree...it will be one degree too much.

~IF~ we are near the terminal limits of global climate change, whether it is Anthropogenic or simply nature's way of telling us we have exceeded our 'use by' date, we should have a definitive, quantifiable indication within the next eight years.

MattJ:
Just to pile on, in addition to the comments by Tom Dayton and Jim Eager ... as John Cook mentioned at the top of this thread, there are some graphs showing runaway and non-runaway positive feedbacks in a comment here.

In all fairness, I have seen lots of people who are under the impression that any positive feedback in the climate system would inherently imply runaway warming, a la Venus. That's not actually the case, however. As long as the feedback factor is small enough, it will just amplify the original warming (or cooling).

During the glacial/interglacial cycles, the primary forcing is changes in the latitudinal/temporal pattern of insolation. This forcing is then amplified by a series of positive feedbacks involving CO2, methane, ice-albedo, dust, etc.

Today, the primary forcing is CO2, complemented to a lesser extent by CH4, N2O, halocarbons, etc. The same feedbacks operate.

All of these are discussed by IPCC and are basic staples of the consensus model of climate change past, present, and future. If John Cook doesn't discuss them in the article at the top of the thread, it's because he's responding to someone else's argument that specifically involves CO2 ... so he focuses on CO2.

If you doubt this, go ahead and type "methane" or whatever into the search box at the top left, and you'll find that all of these factors are discussed in detail on this site. For example, one link that pops up is

My understanding of the reason why there hasn't been a runaway warming event in the past 72 million years is because the pool of available CO2 has been that present in the total biosphere during that entire period (around 280-300ppm). That is to say, even at the height of every past interglacial, the maximum concentration of CO2 in the atmosphere has been less than 300ppm. The combined warming caused by both increased insolation & the natural peak in CO2, in the past has apparently not been sufficient to cause the release of methane hydrate in the Arctic regions. Unfortunately, humans are currently releasing levels of CO2 far above those naturally available in the biosphere-because we're burning CO2 sinks that were buried close to half a *billion* years ago, when CO2 levels were 10 times higher than today, & when the average temperature of the planet was around 6 degrees warmer than now. We are also releasing this CO2 at a rate far, far higher than usually occurs in nature (around 60+ years, compared to over 800 years), which is causing a rate of warming (in degrees per decade) far greater than what we've seen in the past. To the best of my knowledge, these are the reasons why we risk runaway climate change now, but never faced a similar threat in the past!

The usage of the terminology "feedback" is a bit different in other fields than it is often used in climatology. Further, for the commenters here discussing prospects of "runaway warming" and "positive feedback" it is important to distinguish between radiative climate feedbacks and carbon-cycle feedbacks. A few comments are going a bit astray in their descriptions so I will try to focus the posts here down the right path, though this will be mildly lengthy:

First off, a "no feedback" scenario in the context of climate change is one in which the radiative forcing for CO2, solar irradiance, or whatever else is allowed to vary but you hold all variables which are climate-dependent constant (e.g., no ice melts, cloud climatology remains the same). In this case, the only response which is allowed to occur as the temperature changes is an increase in the outgoing longwave radiation (this is the Planck feedback and is a pre-requisite to come back to equilibrium at all). From this it can shown that the sensitivity parameter is inversely proportional to the 3rd power of the emission temperature of the planet, and temperature changes by about 0.25 Kelvin per Watts per square meter forcing. The forcing for a doubling of CO2 is about 4 W/m2 and thus you get ~1 K temperature rise in this simplified case.

It is from this baseline which "positive feedbacks" and "negative feedbacks" are defined. If the total temperature response to a 1 W/m2 forcing is greater than 0.25 K, then we can say the net effect of the feedbacks was to be positive. If the temperature rise from a 1 W/m2 forcing is somewhere between zero and 0.25 K, then the net effect of feedbacks is to be negative.

From this viewpoint the only thing positive feedbacks mean is that the final equilibrium temperature response is amplified relative to the Planck radiation only feedback case (i.e., greater than 0.25 K/W/m2). The individual feedbacks of interest here are primarily the response of water vapor, clouds, the lapse rate, and the surface albedo to global temperature change. This is the case because these things are the main components whose properties are temperature-dependent and because they also modify the energy balance of the planet.

When talking about biological and other carbon-cycle feedbacks, such as ocean outgassing, methane release from the Arctic or deep ocean, changes in vegetation-- this is a bit different because in these cases you're only talking about the rapidity at which you change the greenhouse concentration. The temperature response to a doubling of CO2 depends only on the CO2 forcing and the aforementioned radiative feedbacks. A doubling of CO2 is a doubling of CO2; the only thing ocean outgassing or biological feedbacks do is modify the rate at which you get there.

By the way, all of these things are feedbacks to temperature, not to CO2 (or solar, or whatever) and for the most part the sensitivity of the climate is independent of what causes it to be pushed. It is nonsensical to say "AGW proponents" (whatever this means) say water vapor feedback must be positive or that methane must be released from Arctic permafrost. The positive water vapor feedback emerges from the consequence of well-known thermodynamic relationships between the saturation vapor pressure of a condensable substance in the air, and the temperature. The logic would equally apply to any gas which is condensable on the planet/moon in consideration (CO2 can condense in the Martian poles for example, or methane on Titan). Carbon feedbacks are a bit dicier because there is no theoretical law that mandates that CO2 must be higher in warm interglacials than during cold glacial periods...it just tends to be the case...Whether a carbon feedback takes place could also depend on the initial climate state, so there is no mandate that something which happens from now until a doubling of CO2 must have also happened as you are getting out of a glaciation. Biology, permafrost, methane hydrates,etc all have their own complex physical processes and thresholds

Whether we consider the CO2 change to be a positive or negative feedback to temperature depends on the timescale. Over orbital time periods CO2 tends to rise and fall in sync with temperature, but over longer geological time periods, CO2 tends to accumulate in colder regimes since weathering is less efficient. This is the silicate-weathering control on climate which is thought to be a primary factor in keeping the Earth's climate within a relatively narrow range of possible states in our 4.6 billion year history. You need water and rocks for this to work...concerning Marcus' comment, biology is not a real important control knob on Earth's CO2 concentration. Further, CO2 has been much higher than present in the last 100 million years. Prior to the ice core record you can find climates with many thousands of parts per million CO2, and these tend to be associated with mostly or completely ice free climates. Ever since the formation of the two great ice sheets, the Earth is not quite in a state anymore to be conducive to such conditions anytime soon.

Re: "Runaway Warming"

With this being said, to talk about "runaway" warming we need to define what that means, since colloquial usage of the term is almost always different from scientific usages of the word. In the more laid-back usage, it can mean anything from an extreme amount of warming that pushes the limits of human comfort, it can mean exceeding some socially acceptable amount of warming, it can refer to anomalously high levels of greenhouse gases in the atmosphere, or whatever. It can typically mean whatever you want so long as you are clear with your audience about its meaning so everyone is on the same level.

In the scientific sense, a runaway greenhouse refers to the boiling off of a planets ocean. This occurs in response to a threshold at which the planets outgoing radiation becomes decoupled with the temperature, and when this kicks in, the planet will continue to take in solar energy at a greater rate than it can possibly emit back to space and will warm up until the oceans are lost. The threshold is often called the Kombayashi-Ingersoll limit and describes a flattening off of the radiant emission curve over a range of temperature increases. Once the whole inventory of water is atmospheric-bound (and generally lost to space) the planet can then emit radiation again to balance the incoming energy although it is now at temperatures of many hundreds or many thousands of degrees Kelvin. This clearly never occurred on Earth in the past (even when CO2 was much higher than today or when methane was rapidly released from the deep ocean or Arctic) and it is not something that can even happen today if we burn all the coal and oil. In fact, the runaway threshold is only mildly sensitive to the CO2 concentration and is mostly set by incoming solar radiation and the planets gravity. The planck radiation feedback (sigma T^4) places strong constraints on the range of climates possible for Earth under current solar conditions.

"Runaway Warming" - that's interesting Chris, I'm learning a lot today in various venues. So presumably, by your definition, only Venus and Mars have experienced "Runaway Warming" in our solar system, is that right? And Earth can't.

I had always taken the phrase to refer to the continuing feedback of more CO2 gives higher temps gives more CO2 and so on. And then, in addition, more warming gives release of methane, lower albedo, and so on, so that you get even more warming, and so on. That is, unless you can break the loop by dropping CO2 levels, you will find temperatures rising faster and faster to whatever theoretical maximum is possible given Earth's geography and atmosphere, and at that maximum we are all in big big trouble. It may not be "runaway" to infinity (as it were) but it is runaway as far as the well being of life forms on the planet are concerned.

My concern is that positive feedbacks seem to only ever be applied to greenhouse gases, not to eg the sun. This is inconsistent.

For eg, if we stopped all greenhouse gas emmissions now, we would still get warming for several decades because of all the heat already gone into the oceans. But why can't this also apply to changes in insolation/output from the sun 1750-1950, eg from when the sun stopped increase in output from about 1750-1950s- to the late 20th century, or after the end of ice ages, to swamp the relative effects of greenhouse gases, in both cases?

00

Response: You're completely correct that positive feedbacks don't apply just to greenhouse gases. They apply to any warming whether it be from the sun or greenhouse gases.

So there is a time lag after the sun stops increasing. A paper by Sami Solanki compares the temperature record to solar activity over the last 10,000 years or so. He finds a lag of around a decade - when the solar output changes, it takes around a decade for the temperature to come back to equilibrium.

What happened throughout the 20th Century was the sun warmed in the first half of the century, then levelled off in the 1950s. So what we expect to see if after the sun leveled off in the 1950s, if the sun was the major driver of climate over the 20th Century, we would see global temperatures continue to rise for a decade or two (or three) as it gradually approached equilibrium.

Instead we see the opposite. After the 1950s, we experienced cooling then as we got further away from the 1950s, the planet's energy imbalance actually increased rather than decreased towards equilibrium. So we're going in the opposite direction to what we expect if solar changes was the main driver of climate.

thingadonta - why do you get this idea? The climate models always work on premise that climate is response to all forcings and temperature feedbacks happen irrespective of forcing. See 2nd paragraph of Chris's post above. The estimates of sensitivity from past climate change HAVE to work on basis of solar induced feedbacks. One of the arguments against low sensitivity is that you couldnt get ice age cycle without strong feedbacks as the forcing is so weak.

The question really is about WHICH forcings are most dominant at the moment.

David, the current mainstream paradigm is that this is what happened in Venus' early history. This is the only planet is our solar system that experienced such a fate, although presumably there are many other planets outside our solar system which can support an atmosphere and receive enough solar radiation for this to be relevant.

On Mars, almost the opposite occurred. The climate evolution of Mars is a tug of war between the sun gradually brightening over geologic time, and the loss of its atmosphere. Geologic evidence for the presence of water suggests that the stronger greenhouse effect temporarily won out in its distant past (although quantifying the levels of CO2 or other greenhouse gases needed to get ancient Mars above freezing is a long-standing issue in comparative planetology and not yet possible with current spectral database information). However, the atmosphere has slowly faded away, and today is only a very small fraction of Earth's atmospheric mass. Mars will never again have any significant atmosphere, and thus cannot generate any meaningful greenhouse effect even if what little of it remains is mostly CO2...The planet is now extremely cold, so in no sense can it be said to have experienced a runaway greenhouse. All the water is frozen beneath the Martian sand. It will take a long time for the sun to keep brightening for Martian temperatures to approach Earth-like values.

For Earth, the range of temperature and CO2 feedback variation that we have experienced in the past are rather small from the perspective of planetary climate. Sure they can get you in and out of an ice age (even the PETM which was one of the best examples of a hellish hothouse and abrupt GHG-induced warming was nothing compared to the temperatures observed on Venus or Mercury, and that cooled down relatively rapidly); however there's a strong converging limit as to how much CO2 feedback you're going to get out of the oceans just by raising the temperature. One interesting discussion on this is here. The domain of interest when discussing the CO2 feedback to warming over the glacial-interglacial cycles should not be taken too far outside the bounds of glacial-interglacial cycles, as things are going to change over different timescales and ranges of temperature. It isn't as though temperature and CO2 are going to keep rising forever, and clearly the ice-albedo feedback diminishes with time and goes to zero when there is no more ice. Just as when you drop a bouncing ball to the ground and let it go, eventually the height of each successive bounce decreases with time. Prior to the point when it stops bouncing completely, you get to the point where it just bounces a millimeter or so up and down for a little while and you can still calculate a number for the total distance that ball went up and down over the course of its journey. This is how feedback (radiative or carbon-based) tend to work on Earth, and is quantified in a manner similar to Jim Eager's post in #10. If you define a feedback factor "f" which diminishes with time (so f < 1) then an example converging series looks like 1 + f + (f^2)+(f^3)...(f^n). Eventually you can add up an infinite number of numbers and still converge to a real finite number (!) since f raised to the power of n becomes exceedingly small when f is between zero and one, and n becomes large.

By the way, if you get an hour or so to sit and watch an excellent climate talk on CO2's role over geologic time, you should definitely watch Richard Alley's a href="http://www.agu.org/meetings/fm09/lectures/lecture_videos/A23A.shtml">presentation presentation at the recent AGU meeting. It is very interesting and informative.

A few extra things that can be observed from the Ice core shown in Jo's SH. Look closely at the point where the warming first starts. Temps & CO2 both start to move up at around the same time. It is only later that the Temp trend starts to lead the CO2 trend. Look also at the difference between the warming phase, where CO2 follows Temp quite well vs the cooling phase where the relationship between CO2 and Temps is more indistinct.

This actually matches what we might expect.

At the bottom of the cycle, huge ice sheets cover large areas of the world, resulting in a low Albedo. A Milankovitch cycle kicks things off and Temps & CO2 start to rise. Also not shown here is possible methane release due to melting permafrost at the edge of the ice sheets. Methane is a powerful but short-lived greenhouse gas which then converts to CO2. So methane could give a significant warming while only leaving a small CO2 residual in the ice core. Also, the ice sheets are so thick that it may be millenia before they start to thin enough and break up. An ice sheet 100 metres thick has essentially the same albedo as one 1 kilometre thick. So they are quite likely shrinking in mass for long periods before any significant albedo change cuts in. So a quite likely sequence of drivers during the warming phase is Milankovitch then Methane then CO2 then Albedo Change.

Now look at the cooling phase. The Temp signal looks much noisier during the early stages, and CO2 doesn't drop much at all. In fact it is relatively stable while Temps climb further at the end of the warming then drop. What could drive this?

Consider; The ice sheets have retreated, leaving bare rock. It will take reasonable periods of time for any meaningful amount of soil to be created there. Then vegetation starts to colonise the exposed land. Not just lichens but later forests. Large Carbon stores. So at the end of the warming phase it is quite possible that CO2 levels were being held down by their absorption by the expanding Biomass while Temps are being driven further up by albedo change as the ice sheets really start to collapse.

As things start to cool, colder weather returns and more snowfall. A few metres of snow has the same albedo as kilometer thick ice sheets. So albedo change can now be a driver very early in the process. And as Temp's drop, you would expect the oceans to start reabsorbing CO2. But there is a store of carbon in the extra biomass that grew during the interglacial. As the cooling progresses and this biomass starts to die-back, this is a store of carbon that can be released into the environment, offsetting to some extent the drawdown by the oceans, holding CO2 levels up.

The noisy Temp' signal during the early part of the cooling phase is what you might expect when natural climate varibiality is occuring during the cooling. A 50 year warmer phase for example could easily remelt snow and ice accumulations when they are still relatively thin, resulting in an oscillation of albedo as a consequence of climate variability. This would only settle down once the degree of cooling is greater than natural variability and remelt cannot be completed; then the accumulation of ice would start in earnest.

But none of these kinds of considerations fit into the simplistic meme that 'CO2 follows Temps, so Temps cause CO2'. Sometimes the world of the Climate Sceptics is a comfortingly simple world. Maybe that is its appeal.

MattJ

To your comment about positive feedbacks, the answer is the second - change the gain. In fact, as long as the gain is less than 1, it will always be a limiting feedback. Examples of how the gain is limited in the climate wrt the ice cores. Albedo can only change due to ice melt until the ice is all melted - then no more feedback. And as ice retreats to just the polar regions the feedback is declining anyway. Similarly albedo change during the cooling phase is limited since ice sheets simply can't spread that far over water. Co2 gain is limited during warming by the logarithmic nature of its radiative effect. Similarly, as cooling progresses the reduction in the volume of the oceans due to sea level fall because more ice is forming on land starts to limit how much CO2 can be bound up in the oceans. So too biomass decline in cold climates will limit the amount of carbon stored in biomass, making it harder to sequester CO2. In the longer time scale, chemical weathering of rocks that removes CO2 from the atmosphere via the formation of Carbonic Acid will be slower in cold climates, faster in hot ones. And balanced against this is the ongoing slow outgassing of CO2 from vulcanism.

During the warming increases significantly the amount of shelf seas, Epeiric arise (epicontinental sea - in the Cretaceous).
Oolite disposal of CO2 is maybe more efficient, maybe faster than by solubility in cold oceans ...
Another eight thousand. years ago, Lake Chad had an area of the Caspian Sea ...

Recent trend in the global oceanic sink for CO2, Quere, 2009:
"On a time-scale of decades, the global oceanic sink for CO2 is limited primarily by the rate at which oceanic circulation transports carbon from the surface to the deep ocean."
"The exact fraction absorbed by the oceans depends on the re-organisation of the natural carbon cycle. Evidence from the geological past suggests that the oceans store less CO2 when the earth's temperature is warm. It is thought that the reduced ocean storage is driven by changes in the Southern ocean circulation, although the exact mechanism is NOT YET RESOLVED. [??]."

As far as I know, no scientist doubts that CO2 is a greenhouse gas. The physics of the gas is well-determined by lab experiements. Adding CO2 increases temperature logarithmically, So if the ordinary behavior of CO2 is what occurs in the atmosphere, we would expect doubling CO2 to cause about 0.75 degrees of warming. The "CO2 crisis" comes from a theory that something in the atmosphere multiplies the effects of CO2 above it's ordinary physical greenhouse effect. The multiplier is claimed to be water vapor, which is theorized to increase CO2 temperature effects by a factor of three. There is no defense of crisis theory in the claim that CO2 behaves like everyone agrees it does. Moreover, claims that CO2 was the cause of past interglacial warming, per Al Gore, are wrong. It was the effect, not the cause. It added a little to the warming as we would expect.

@ Roy Latham #26:"So if the ordinary behavior of CO2 is what occurs in the atmosphere, we would expect doubling CO2 to cause about 0.75 degrees of warming."
Where did that figure come from? Do you have a reference?

"The "CO2 crisis" comes from a theory that something in the atmosphere multiplies the effects of CO2 above it's ordinary physical greenhouse effect. The multiplier is claimed to be water vapor, which is theorized to increase CO2 temperature effects by a factor of three"
Do you have references for this? It was my impression that the "positive feedback" effect (the "multiplier") came from the fact that more CO2 -> higher temperature -> more CO2 (released from ocean) -> etc. But I'm no expert.

"Moreover, claims that CO2 was the cause of past interglacial warming, per Al Gore, are wrong." Do you have references for this? Did Al Gore (or anyone else) claim that CO2 was THE cause of past interglacial warming?

The multiplier is claimed to be water vapor, which is theorized to increase CO2 temperature effects by a factor of three. There is no defense of crisis theory in the claim that CO2 behaves like everyone agrees it does.

Beyond the fact that there's a lot of good reasons to expect relative humidity to, on average, remain roughly constant as temperatures warm ...

There are detailed satellite observations to back it up, as NASA reported last year. A very large number of observations at various altitudes checked against model predictions showed that water vapor feedback was operating almost exactly as models predict.

robhon:

Roy Latham... I don't know where you get the 0.75C for doubling CO2. There are at near a dozen papers listed on this very website that put that figure closer to 3C.

He's talking about direct warming without feedbacks, which actually is "oneish" C, not 0.75C. The 3C figure is due to feedbacks, the major one being water vapor, as Roy points out. However, far from there being "no defense" of this, as I mention above, detailed satellite observations strongly support it.

Roy says:

Moreover, claims that CO2 was the cause of past interglacial warming, per Al Gore, are wrong. It was the effect, not the cause. It added a little to the warming as we would expect.

I doubt Al Gore misstated the science as badly as Roy says, but it doesn't matter, we care what scientists, not Gore, have to say. And scientists don't claim CO2 was the cause of the end of past ice ages. Rather, it's a feedback to the end of Milankovich cycles which, as you say, adds to the expected warming. Though more than "a little".

dhogaza.... Actually, I just went back and was looking through Knutti 2005 and they say in the introduction, "Atmospheric CO2 is prescribed directly in the idealized scenarios used here, other forcings are not considered."

gallopingcamel,
The problem with Hocker's argument was that he was taking a correlation and using that to make a causative argument (even worse, the things that he claims are causative are not part of his correlation). When it comes to CO2 lag scientists make no such claim. The models for temperatures and CO2 level change over these time periods are built up from physics, the historical data only acts as a confirmation of the predicted relationships. This is the appropriate way of using correlations: as evidence for a particular physical explanation, not the source of explanation itself.

In this case, the historical data is consistent with what is predicted by the physical models: according to the models there should be a lag, so the lag supports the models. As such, if you want to criticize the models you'll have to address the physical assumptions, not correlations in the historical data. Otherwise, you are making the same error that Hocker is making.

Marcus at 11:05 AM on 21 June, 2010
"My understanding of the reason why there hasn't been a runaway warming event in the past 72 million years is because the pool of available CO2 has been that present in the total biosphere during that entire period (around 280-300ppm). That is to say, even at the height of every past interglacial, the maximum concentration of CO2 in the atmosphere has been less than 300ppm."

Marcus, i think you would find that what you have written is true for the 2.5mybp, and in all probability out to around 15mybp... but i think you would find that at around as little as 45-50mybp, it was around 900ppm(when ice first started forming on Antarctica) It was continental drift that killed the last hot house and brought the globe into the present ice house, and basically it lead to a gradual burial o carbon from this period(45mybp) until 2.5mybp when the planet went into its glacial interglacial cycles, with the co2 around that 280-300ppm.

My apologies Joe Blog. What I meant was that-at least as of the Quaternary Era (about 3 Mybp)-we've been in a relatively CO2-constrained environment (>300ppm), & this is why we've not had a runaway waring event since then. Apologies for the confusion!

Once again, about how ...
... with great certainty, John Cook says:
"As the ocean warms, the solubility of CO2 in water falls. This causes the oceans to give up more CO2 into the air."
"So the CO2 record is entirely consistent with the warming effect of CO2. In fact, CO2 warming explains both the dramatic changes in temperature in the Earth's past and how temperature change ..."

Glacial – interglacial atmospheric CO2 change ..., Skinner, 2006:

"Although it is clear that changes in atmospheric CO2 have remained tightly coupled with global climate change throughout the past ∼730000 years (Siegenthaler et al., 2005), the mechanisms responsible for pacing and moderating CO2 change remain A MYSTERY. The magnitude of the marine carbon reservoir, and its inevitable response to changes in atmospheric CO2 (Broecker, 1982a), guarantees a significant role for the ocean in glacial – interglacial CO2 change. Based on thermodynamic considerations, glacial atmospheric CO2 would be reduced by up to 30 ppm simply due to the increased 5 solubility of CO2 in a colder glacial ocean; however this reduction would be counteracted by the reduced solubility of CO2 in a more saline glacial ocean and by A LARGE REDUCTION IN THE TERRESTRIAL BIOSPHERE under glacial conditions (which would release carbon to the other global reservoirs) (Broecker and Peng, 1989; Sigman and Boyle, 2000). The bulk of the glacial – interglacial CO2 change therefore remains to be explained by more complex inter-reservoir exchange mechanisms, and the most viable proposals involve either the biological- or the physical “carbon pumps” of the ocean. Indeed it appears that whichever mechanism is invoked to explain glacial – interglacial CO2 change must involve changes in the sequestration of CO2 in the deepest marine reservoir ..."

Quantifying the roles of ocean circulation and biogeochemistry in governing ocean carbon-13 and atmospheric carbon dioxide at the last glacial maximum, Tagliabue et al., 2009,

"Overall, we find that while a reduction in ocean ventilation at the LGM is necessary to reproduce carbon-13 and carbon-14 observations, this circulation results in a LOW net sink for atmospheric CO 2. In contrast, while biogeochemical processes contribute little to carbon isotopes, we can attribute over 90% of the change in atmospheric CO 2 to such factors. The lesser role for circulation means that when all plausible factors are accounted for, over half [!!!] of the necessary CO 2 change remains to be explained. This presents a SERIOUS CHALLENGE TO OUR UNDERSTANDING of the mechanisms behind changes in the global carbon cycle DURING THE GEOLOGIC PAST."

Modelling atmospheric CO 2 changes at geological time scales, François et al., 2005 ;
"Long-term carbon cycle models ARE STILL IN THEIR INFANCY. The major areas for improvement in these models ..."

The scope of our ignorance (The low CO2 glacial ocean as a reverse paleo-analog for the future high CO2 ocean, Heinze, 2009) and the uncertainty is huge: Climate–Carbon Cycle Feedback Analysis: Results from the C4MIP Model Intercomparison (2006) - 29 authors analyzed through 11 models as well as changes to the absorption of CO2 into the oceans and soils as a result of warming. Variance, difference in the results (Figure 1) as the land for the year 2100 is 17 Gt C / year (!), the oceans: 7 Gt C / y!

Building on this area of uncertainty for the calculation of positive feedback for p.CO2 - it's just a misunderstanding ...

Probably the "biogeochemical cycles", that processes are, however, decisive - biological feedback. It's biosphere determines the amount of CO2 in the assessment. Hence, shortening, often for thousands of years, a cool ocean does not equal - a little CO2 in the atmosphere (and vice versa) ...

... "In IPCC scenarios it is assumed that far more fossil reserves would be burnt than is physically recoverable. Using an eddy diffusion ocean model, the IPCC HAS GROSSLY UNDERESTIMATED the future OCEANIC CO 2 uptake. Hardly coping with BIOMASS response and taking a double to treble temperature sensitivity, all this has led to an IPCC error factor of up to an order of magnitude." (Dietze, 1997, continuous update - 2010).

According to Sourcewatch, Peter Dietze is an electrical engineer, not a climate scientist. He has published no climate-science research in the peer-reviewed literature.

Citing someone like that isn't likely to convince the science-savvy participants here.

Electrical engineers who know nothing about climate science but still consider themselves climate-science experts are a dime a dozen. I know a few personally. They may be experts in their own narrow specialties, but they have little appreciation of the limits of their expertise.

"Abstract. So far, the exploration of possible mechanisms for glacial atmospheric CO2 drawdown and marine carbon sequestration has tended to focus on dynamic or kinetic processes (i.e. variable mixing-, equilibration- or export rates). Here an attempt is made to underline instead the possible importance of changes in the standing volumes of intra-oceanic carbon reservoirs (i.e. different water-masses) in influencing the total marine carbon inventory. By way of illustration, a simple mechanism is proposed for enhancing the marine carbon inventory via an increase in the volume of relatively cold and carbon-enriched deep water, analogous to modern Lower Circumpolar Deep Water (LCDW), filling the ocean basins. A set of simple box-model experiments confirm the expectation that a deep sea dominated by an expanded LCDW-like watermass holds more CO2 , without any pre-imposed changes in ocean overturning rate, biological export or ocean-atmosphere exchange. The magnitude of this “standing volume effect” (which operates by boosting the solubility- and biological pumps) might be as large as thecontributions that have previously been attributed to carbonate compensation, terrestrial biosphere reduction or ocean fertilisation for example. By providing a means of not only enhancing but also driving changes in the efﬁciency of the biological- and solubility pumps, this standing volume mechanism may help to reduce the amount of glacial-interglacial CO2 change that remains to be explained by other mechanisms that are difficult to assess in the geological archive, such as reduced mass transport or mixing rates in particular. This in turn could help narrow the search for forcing conditions capable of pushing the global carbon cycle between glacial and interglacial modes." (emphasis added)

I don't think this study says quite what Arkadiusz Semczyszak wants it to say.

Actually, I just went back and was looking through Knutti 2005 and they say in the introduction, "Atmospheric CO2 is prescribed directly in the idealized scenarios used here, other forcings are not considered."

So, they get 1.4C to 6.5C without other forcings.

True - those figures are derived by including estimated feedbacks to CO2 forcing. They don't consider other forcings.

Arkadiusz, is there such a thing as "official scientific reviewer" in IPCC terminology? I remember the term "expert reviewer", a status in fact so open that it does not mean much. Are you talking about the same thing? We already had that conversation about Dip Phil Courtney, who is just a PR guy by trade.

Full information indeed is necessary, as in the Maxwell Bay sediment core story.

I was looking at the Vostok graphs at Nova's site (specifically the last one), and was wondering about a couple of things. Perhaps I should ask this first, though--is her graph a valid one to look at, or is there a better one?

There are a few places where the temp and CO2 lines go in opposite directions, or don't seem to follow the lag rule. Around 50,000 years ago they don't match up well. 160,000 to 170,000 years ago there are several temp spikes with no CO2 movement. About 375,000 years ago temp spikes while CO2 continues downward.

I realize these are only a few places out of hundreds of thousands of years of history, and you've said before that CO2 is not the only climate driver, and it's possible that the time resolution isn't detailed enough to show all of the movements, but I am wondering what effects could suspend or negate the CO2 lag? Is the concentration change in CO2 not enough to overpower other effects?

I haven't checked the JoNova charts, but if you can drive Windows Excel or other chart/spreadsheet programs you can download more up to date data from the NOAA Paleo (Ice Core) website and make your own charts. For 800k years of CO2 look at Luthi 2008, EPICA Dome C data series (he has a composite including Vostok), and for temperature look at Jouzel 2007 from the same site. I think they have the most consistent EDC3 ice age/gas age dating. This and the quoted uncertainties are something to strongly consider when judging lag.

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